Process and apparatus for pasteurizing milk



Nov. 21;, 1946. H EGLI 2,411,681

PROCESSA AND APPARATUS FOR PASTEURIZING MILK A Filed Feb. 19,. 1941 Parenteel Nov. 26, 1946 2,411,681 PRoEss'AND AriARA'rUs Fon *y .PAs'rEUmzrNG MILK nulareich Egli, alt'iniorejMd. n Application February 19, 19111, serial No. 379,731

This ,invention relates 4to a method and an apparatus for vhandling ,and storing of fluids and has for its principal object the provision of lmeans to handle and store, with a minimum amount of foaming and shrinkage, aliquid composed Vof a plurality of ingredients, such for example as milk.

YAn important object of the present invention is the provision of a system for pasteurizing milk in an eflicient manner and under conditions which minimize the presence of bacteria in .the nished product. While for convenience lof illustration and descriptionof the process, the apparatus will be described in connection with a system for pas- 'teurizing milk, it should be obvious that .the inven- 'A Vstill further object of the present invention consistsof a method of storing fluids, the' lower vfluid being atene temperature and the upper fluid being at a diferent' temperature. A still further object lies in the provision of a system of'holding milk during .thepasteurizing process in a plurality of containers each cross-connected to the others so that the pressure on each batch is identical.

Still further minor lobjects of 'the invention will ioclaims. (Cres-211) be apparent from the following description and was'set forth in the claims, A

The/drawing illustrates a system primarily intended for the pasteiirizing of milk. The apparatus illustrated in the figurel con sists of a plurality of containers' Illa to Ie each "receiving hot milk from a main line II feeding Vr`to branches' I2 leadingto e-ach of theseveral vats or tanks which are of Well: known type and may 'ibe jacketed `or insulated as indicated atI4l in connection with container |01). The advantage of Va plurality of containers Vlies in the' provision of continuous flow, one container is'iilled as another is emptied. The several branch lines I 2 each lead leadingr from a Well `I8' discharges the milk through 4branch lines I 9 to thejexit header 20 when permitted by the electrically controlled exit valve 2I. It might be noted here that while the `valves I5 and 2l maybe mechanically operated Yor may `be electrically controlled in any manner it is my preferencethat these valves shall'beop- .erated by timealone;v

valves.

,)I'he particular apparatus` .for warming the milk is somewhat immaterial, steam, electric connections, or hot water being suitable agents. My

preferencev is largely in favor of hot Water because of its easy control. The hot water enters at 24, past a stop valve 25 and a control valve 26, the latter being `governed by a thermostat 21 set in the vat or container at a convenient height preferably nearer the bottom .than the top. Under each containerthere is a suitable heatingY deviceindi'cated generally by the numeral 30 which inthe case vof hot Water would be a simple jacket having yanzentry valve 3 I and an exit valve 32 leading .to 4the return conduit 33 which leads to the heater, not shown, which delivers the Water to the pipe 24. By` placing the heater under the tank the rising ofthe warmer particles by change of ,density with vincreased Itemperature takes the place of an otherwise necessary agitating means.

It is desired to'have the temperature ofthe fluid above the liquid at all times greater than that of .the lower fluid, the pressure of the fluid vfpipe 40 as shownand might use electrical resistance wires or steam or hot Water, preferably va liquid controlled'by a stop valve 44 and an electrical control valve 45'which admits the heating v fluid at such a' rate as to keep the air at the chosen ftemperature, for example, at F. at the tops of the containers, the pressure varying in accordv'ance with the hydrostatic pressure on the milk or other liquid, for example, it might be ve pounds 'corresponding to la lift of over ten feet. The hot 'wa-ter, if used, might be as highvas 180 F.,'the famount vbeing controlled bythe valve'45 and by the valve 48', which latter however need 'onlybe a stop' valve for emergency use being located in the returnline 49 which discharges back to the lheater, not shown, kwhich supplies the pipe 42. y

' part ofthe present invent-ion.r Thepanel is connected by the cable 5I with each inlet valve and isconnected by the cable 52 with each of the exit The thermostat 56 extendinginto the air space above the liquid in the last container Ille actuates mechanically or electrically, preferably `the latter, the heat supply control valve 45 through the Wire 51 which may,'but need not, be

tolbe inseparablefromthe process of pasteurizing 'por s incapable of taking up further moisture and, corresponding to its pressurey counteracts' the vapor pressure of the liquid and consequently Y avoids shrinkage.

In my process foaming is minimized by increasing the surface tension so as to prevent the gathering of the active colloids to spread in lms sufficiently tough and elastic as to keep the globules of gas from coalescing. In froth or foam an enormous area of gas surface is produced as the gas phase is dispersed as minute bubblesin the liquid phase.. The gas bubbles persist. for some time. owing to the presence of milk colloids in a solid condition.v Foamingv tends to convey bacteria, is wasteful, and tends to hinder eicient handling of the milk or the uid being treated. As stated in Department of Agriculture Circular 108, March 1930, foaming in pasteurizersr may present a public health problem. hence its. avoidance is of paramount importance. By having relatively deep containers with increased pressure above the liquid therein, the gap or diierential between the boiling point of the water at the bottom of the tank and` that of the water near the top of the tank is reduced so a greater surface tension of the liquid is obtained and with it. a substantialv absence of foaming anda material reduction of skin formation. A simple experiment will show that when a foaming liquid is discharged. into a container held at a positive or above. atmosphere pressure an appreciable amount of the foaming at once collapses with coalescence of the occluded gas bubbles.l

The temperature con-trol is essential. in the pasteurizing process; also in holding processes of beverages consisting of mixed ingredients. At times it is desirable to maintain a slightly higher temperature. at the exposed. surface to air pressure of the contents than that of the contents itself. For this: reason the pressure. equalizing conduit, which is cross connected withV all con-- tainers, is independently controlled. as to temperatures governed by the. thermostat. inserted into the air space abovev the liquid line. in. the

containers.

Further details of the invention can. best. be understood through a description. of the operation of the mechanismy when the process comprises the pasteurizing4 of milk. In the. drawing the three center containers are each` full and are being held at chosen ten-rperaturer and pressure both for thev milk at the bottom and for the air above.- The nal. containerr Ite isbeing emptied and the -rst containerma is being filled, the milk at atemperature; of say 145.o F; entering th-roughpipe Il", branch linei2, past electrically controlled entryvalve t5 and tank pipeA` I6 which is secured toV the removable cover 6l) which' carries a. thermometer 6l' and a relief valve B2i as well as the entryV andexit valves- This,A milk is under pressure which might be added by a pump but. preferably the pressure is above atmospheric but of. course. isf lower than the pressure head on the milk. However, asA air isf discharged through' pipe` #il to the heated- Y remain constant.

4 header 40 in the rst tank it is entering the nal tank Ille at precisely the same rate and the same temperature and pressure, The valve 62 on each container insures that the temperature of the air or other iluid at the top of the container shall The thermostatically operated valve opens at a chosen temperature, say 148 F. and lets out the air which at this temperature is colderV than desired and'by lowering-the pressure causes air' to enter fromA the heated air line 43 which itself is kept at a constant pressure by the ordinary mechanism and its temperature is maintained by the automatic Valve controlled by' thermostat 56 in the removable top of containerv Ille. As is quite obvious, the valve 62 will open. upon a rise of temperature when the system is used for chilling the liquid as in that case theY temperature of the upper fluid will be lower than that of the liquid beneath, and the heater 30 will be a refrigerating device.

As milk rises in the tank AIlia it receives heat from the heater in contact with only a portion of the bottom of the container.A The thermometer t5 indicates the temperature and the adjacent thermostat operated by the temperature opens or closes the valve 26,' thus insuring precisely the correct temperature in the containers at all times.

Assuming the chosen' temperature for pasteurizing is and the' cycle is one hour, the thermostat 21 will operate to close the valve 26V at a temperature of 146, thus insuring the temperature of the milk. The temperature of the' air is greater and this is' controlled' -by the Valve 62 as` noted. With the arrangement illustrated it ,would take 12 minutes to empty or tov fill any one of the tanks, these two operations always being simultaneous in the'series.. Any one tank or container which began illing at the even hour startsto empty 36 minutes after' it has been filled, i. e., at 48minutes after the hour, thus completing the hour when it is' fully empty. While I nd it best to have a separate temperature control of the compressed air above the liquid in the holding containers, there seems to be no need for an independent control of the temperature in the various heaters 3'0, noris there need for individual control of the heat in the several' jackets 43 as the pressureV in' the pipes 4l) and 4l is automatically maintained by the pressure equalizing features described'. As previously'suggested the sameequipment', with somewhat differentconnections, also serves at otherv times to chill the milk, the mains 431 and 24 now carrying a refrigerant.

What I claim is:

1. The processof minimizing frothing inchangi'ng a liquidvv into containers which consists' in providing two containers with the liquid' beneath a fluid at a pressure above atmospheric crossconnecting th'e'fluids to equalize. their pressure, and introducing further liquid under pressure into one container as liquid at theI same rate is withdrawn from the other container.

2. The process of claim 1V in which .the temperature of the fluid is maintained at a. predetermined degree in each containerrand` the furtherv liquid isv introduced ata substantially constant pressure.

3. The process. of claim, 1 in whichy the fluid is compressed air, the temperature of which is maintained atthe sameV degree,'in each contai-ner,` and thev further liquid is introducedy at a `substantially constantv pressure;

4. A constant pressure liquidholding system comprising a plurality of closed containers, an air conduit, means for holding air in said conduit at a chosen pressure and temperature, means connecting the conduit with each of the containers, a relief valve on each container discharging air from vthe container when its temperature departs from a chosen value whereby air at the chosen pressure and temperature will now into the container from the air conduit.

5. The device of claim 4 with means for charging a liquid under pressure to any one of the containers, and means for discharging another of said containers at the same rate as the first container is charged.

6. In combination a jacketed container, means for maintaining a uid under pressure in the container, a container relief valve, opening to discharge the uid if the temperature of the fluid falls below a chosen amount, means for charging and discharging a liquid into the container below said fluid, including piping partly within the container and time operated valves in the charging and discharging piping.

7. The process of claim 1 in which the fluid is compressed air saturated with water vapor, the liquid is milk, and the air driven from one containerby the incoming milk is discharged into said other container which is simultaneously being emptied, whereby the water vapor saturated air is reused.

8. In combination, a series of closed containers, each having a bottom, heating means below each container and having horizontal dimensions less than those of the bottom, a liquid distributing system leading to each container, including an entry pipe and an exit pipe in each container, having their bottom open ends near the bottom of the container, time controlled valves governing the ow through the entrance pipes and the exit pipes, an air pipe having an open end near the top of each container and Within the same, an air conduit joining all of said air pipes, means for heating the air in the conduit controlled by the temperature adjacent the open end of one of the air pipes, means for maintaining a pressure above atmospheric in the conduit and the air pipes, and means for charging liquid through the distributing system and simultaneously forcing air through the closed path of the conduit and air pipes, whereby shrinkage of the liquid is min-V imized and the paths taken by the uid and the liquid are widely separated, the air entering and leaving the containers at the top only Aand the liquid entering and leaving the containers at the bottom only.

9. The device of claim 8 in which the heating means below the containers is controlled by the temperature within the container separately of the heating means for the air conduit, and a relief valve on one of the containers discharges air from above the liquid should such air fall below a predetermined degree of temperature.

10. In a milk pasteurizing system, a jacketed container, means for admitting heated air under pressure to the container above the milk, means for releasing air from the container as it falls below a predetermined degree of temperature, and time controlled means for admitting milk to the container and for discharging milk therefrom, said last means including piping, the open ends of which are widely spaced from the open ends of the air admitting and releasing means, whereby to avoid passage of milk through any part of the air system.

HULDREICI-I EGLI. 

